Add generic PaletteDelegate code.

ash/mus/shell_delegate_mus.cc

Index: ash/mus/shell_delegate_mus.cc
diff --git a/ash/mus/shell_delegate_mus.cc b/ash/mus/shell_delegate_mus.cc
index cf45d1d9c0c243cecbebee77666a3d37adb9a1f3..32ffcd4e562f5ded27b1835324b0600cc4ddb256 100644
--- a/ash/mus/shell_delegate_mus.cc
+++ b/ash/mus/shell_delegate_mus.cc
@@ -8,6 +8,7 @@
 
 #include "ash/common/gpu_support_stub.h"
 #include "ash/common/media_delegate.h"
+#include "ash/common/palette_delegate.h"
 #include "ash/common/pointer_watcher_delegate.h"
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/system/tray/default_system_tray_delegate.h"
@@ -196,6 +197,11 @@ MediaDelegate* ShellDelegateMus::CreateMediaDelegate() {
   return new MediaDelegateStub;
 }
 
+std::unique_ptr<PaletteDelegate> ShellDelegateMus::CreatePaletteDelegate() {
+  NOTIMPLEMENTED();
+  return nullptr;
+}
+
 std::unique_ptr<PointerWatcherDelegate>
 ShellDelegateMus::CreatePointerWatcherDelegate() {
   NOTIMPLEMENTED();